Traffic stops are the most common way people in the US encounter police. Research by the Stanford Open Policing Project, which analyzed close to 100 million stops, found that Black drivers were stopped more often than white drivers. Once stopped, they were searched more often, even though searches of white drivers turned up contraband at a similar or higher rate.
The law makes this easy. In Whren v. United States (1996), the Supreme Court ruled that police may use any minor traffic violation to stop a car, even if the real motive is something else. That allows pretext stops for a broken taillight or a tinted window.
The danger is old. Black travelers used The Green Book from 1936 to the 1960s to avoid hostile towns and police. Today, routine stops have ended in police killings, including Philando Castile in 2016. Some cities now limit stops for minor equipment violations to reduce harm.